Vinyl aromatic resins such as, for example, rubbermodified polystyrenes are useful thermoplastic compositions. However, these resins burn readily and thus cannot be used in applications where flammability resistance is desirable. Attempts to eliminate this deficiency include blending certain compounds into the resin. For example, Japanese Patent Application No. 52-838 assigned to Daiichi Seiyaku Company, Ltd., discloses flame retardant compositions such as nuclear brominated and chlorinated polystyrenes, halogenated polyolefins and antimony trioxide which can be blended with a variety of thermosetting and thermoplastic resins including polystyrene.
Another method to eliminate this deficiency includes preparation of rubber-modified resins by copolymerization in the presence of a rubbery polymer of a monomer mixture consisting of (a) a nuclear brominated styrene and (b) one or more monomers selected from among vinyl aromatic compounds, vinyl cyanides and (meth)acrylic acid esters. See in this connection, Japanese Patent Application No. 53-10689 assigned to Japan Synthetic Rubber Company, Ltd. However, in addition to the required presence of the latter class of compounds, i.e., group (b) monomers, achievement of a V-O rating as determined by the UL-94 test required the addition of flame retardant synergist such as antimony trioxide.